Lesson Notes By Weeks and Term - Senior Secondary 2

Halogens I

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TERM: 2ND TERM

WEEK SIX

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:        

Subject: Chemistry

Topic:-        HALOGENS 1

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Electronic configuration of Halogens
  2. Physical properties of Halogens.
  3. Chemical properties of Halogens.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher discusses halogens and their electronic configuration.

Students pay attention

STEP 2

EXPLANATION

He explains physical properties of halogens to the students.

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He discusses the chemical properties of halogens

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

HALOGENS

Halogens are a group of elements in Group 17 (VIIA) of the periodic table. The halogen group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements share some common characteristics:

  1. Valence Electrons: Halogens have seven valence electrons in their outermost energy level.
  2. High Reactivity: Halogens are highly reactive and tend to gain one electron to achieve a stable, noble gas electron configuration. They are powerful oxidizing agents.
  3. Physical States: Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine and astatine are solids.
  4. Color: Halogens exhibit distinct colors. For example, chlorine is a greenish-yellow gas, bromine is a reddish-brown liquid, and iodine has a violet vapor.
  5. Halide Ions: Halogens can form halide ions (F-, Cl-, Br-, I-) by gaining one electron.

The electronic configuration of halogens.

Physical Properties of Halogens

  1. State at Room Temperature:

   - Fluorine and chlorine are gases.

   - Bromine is a liquid.

   - Iodine is a solid.

   - Astatine is a rare, radioactive solid (its properties are less well-studied due to its scarcity).

  1. Color:

   - Fluorine: Pale yellow.

   - Chlorine: Greenish-yellow.

   - Bromine: Reddish-brown liquid.

   - Iodine: Violet solid.

   - Astatine: Properties less well-defined due to its scarcity.

  1. Odor:

   - Fluorine: Pungent.

   - Chlorine: Strong and suffocating.

   - Bromine: Sweet and unpleasant.

   - Iodine: Sublimes to produce a distinctive smell.

   - Astatine: Limited information due to its scarcity.

  1. Melting and Boiling Points:

   - Generally, melting and boiling points increase down the group.

   - Exception: Bromine has a lower boiling point than chlorine due to its inter-molecular forces in the liquid state.

Graduation Down the Group

  1. Atomic Size:

   - Increases down the group due to the addition of energy levels.

  1. Atomic Mass:

   - Increases down the group.

  1. Density:

   - Generally increases down the group.

  1. Ionization Energy:

   - Decreases down the group due to the increase in atomic size.

  1. Reactivity:

   - Decreases down the group in terms of reactivity with other elements. Fluorine is the most reactive halogen.

Chemical Properties of Halogens

  1. Reactivity:

   - Halogens are highly reactive and tend to undergo redox reactions by gaining one electron to achieve a stable electron configuration.

   - Reactivity decreases down the group; fluorine is the most reactive halogen.

  1. Formation of Halide Ions:

   - Halogens readily form halide ions by gaining one electron. For example, chlorine forms chloride ions (Cl-) when it gains an electron.

Graduation Down the Group

  1. Reducing Ability:

   - Reducing ability decreases down the group. Fluorine is a powerful oxidizing agent.

  1. Acid-Base Properties:

   - Halogens can act as both acids and oxidizing agents. As you go down the group, the acidic nature decreases.

EVALUATION: -  Write down the electronic configuration of halogens.

                          - Mention three physical properties of halogens,

                          - Mention three chemical properties of halogens.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively